Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

The following formula computes the read IOTEMP of a given file:
IOTEMP = (bytes of the file that are read in the PERIOD) /
(PERIOD in hours * size of the file in bytes)
The write and read/write IOTEMP are also computed accordingly.
The following formula computes the average read IOTEMP:
Average IOTEMP = (bytes read of all active files in the last h hours) /
(h * size of all the active files in bytes)
h is 24 hours by default. The average write and read/write IOTEMP are also
computed accordingly.
In the example snippet, the value 1.5 is the multiple of average read IOTEMP over
the last 24 hours across the whole file system, or rather across all of the active
inodes whose activity is still available in the File Change Log (FCL) file at the time
of the scan. Thus, the files’ read IOTEMP activity over the last 6 hours is compared
against 1.5 times that of the last 24 hours average activity to make the relocation
decision. Using this method eliminates the need to give a specific number for the
<IOTEMP> or <ACCESSTEMP> criteria, and instead lets you specify a multiple of the
Average temperature. Keeping this averaging period longer than the specified
<PERIOD> value normalizes the effects of any spikes and lulls in the file activity.
You can also use the Average criteria with the <ACCESSTEMP> criteria. The purpose
and usage are the same.
You determine the type of the average by whether you specify the Average criteria
with the <IOTEMP> or with the <ACCESSTEMP> criteria. The Average criteria can be
any of the following types, depending on the criteria used:
■ read Average IOTEMP
■ write Average IOTEMP
■ rw Average IOTEMP
■ read Average ACCESSTEMP
■ write Average ACCESSTEMP
■ rw Average ACCESSTEMP
The default Average is a 24 hour average temperature, which is the total of all of
the temperatures available up to the last 24 hours in the FCL file, divided by the
number of files for which such I/O statistics still exist in the FCL file. You can
override the number of hours by specifying the AveragePeriod attribute in the
<PLACEMENT_POLICY> element. Symantec recommends that you specify an
AveragePeriod attribute value only if you are using solid state disks (SSDs).
Administering SmartTier
File placement policy rules
362